1. Field of Technology
The present invention relates to a sheet supply apparatus wherein an air jet is blasted to the edges of stacked sheets, which are suctioned to the suction surface made of a conveyance belt and others, whereby these sheets are fed out. The present invention relates particularly to a sheet supply apparatus wherein air outlet elevation control is performed in conformity to the result of detecting the presence or absence of a sheet suctioned to the suction surface.
2. Description of Related Art
A pneumatic sheet supply apparatus has been employed as the sheet supply apparatus for such an image forming apparatus as a photocopier. In the pneumatic sheet supply apparatus, an air jet is blasted to the lateral end faces of stacked sheets, and the sheet raised by air is suctioned to the suction surface such as a perforated belt wherein air inlets for suction of air are formed. The belt is driven to convey the sheet.
In the pneumatic sheet supply apparatus, if there is an air outlet above the upper side of the stacked sheets, a thick paper cannot be effectively raised because air jet fails to be blasted to the side of the sheet effectively, although a thin sheet can be raised.
On the other hand, if there is an air outlet below the upper side of the stacked sheets, a thick paper can also be raised. In the case of thin sheets, however, they tend to be raised as a bundle of sheets. When an air jet passes through the lower side of the raised bundle of sheets, the sheets cannot be easily separated from one another.
One of the proposals made to solve this problem is the technique wherein a mechanism for elevating an air outlet is used, and the elevation of an air outlet is controlled in conformity to the method of estimated control of time and others (Japanese Unexamined Patent Application Publication No. 2006-168933).
However, in the conventional pneumatic sheet supply apparatus, the air outlet is raised in conformity to estimated control. This involves a possible suction failure wherein sheets are not suctioned onto the suction surface, as well as possible multiple feed, wherein a plurality of sheets cannot be separated from one another, and the overlapped sheets are conveyed in the state of being suctioned onto the suction surface.
In view of the problems described above, it is an object of the present invention to provide a sheet supply apparatus wherein positive suction of sheets is ensured independently of the type thereof and the suctioned sheets can be separated from one another, a sheet supply unit provided with the aforementioned sheet supply apparatus, and an image forming apparatus.